Research ArticleMATERIALS SCIENCE

Writing in the granular gel medium

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Science Advances  25 Sep 2015:
Vol. 1, no. 8, e1500655
DOI: 10.1126/sciadv.1500655
  • Fig. 1 Granular gel as a 3D writing medium.

    (A) A microscale capillary tip sweeps out a complex pattern as material is injected into the granular gel medium. Complex objects can be generated because the drawn structure does not need to solidify or generate support on its own. (B) As the tip moves, the granular gel locally fluidizes and then rapidly solidifies, leaving a drawn cylinder in its wake. The reversible transition allows the tip to traverse the same regions repeatedly. (C) The soft granular gel is a yield stress material, which elastically deforms at low shear strains and fluidizes at high strains. (D) Stress-strain measurements reveal a shear modulus of 64 Pa and a yield stress of 9 Pa for 0.2% (w/v) Carbopol gel. (E) The cross-sectional area of written features exhibits nearly ideal behavior over a wide range of tip speeds, v, and flow rates, Q. The trend line corresponds to the volume conserving relationship, Embedded Image.

  • Fig. 2 Stable writing in the granular gel medium.

    (A) Injection tip filled with fluorescent microsphere suspension, imaged under UV illumination. (B) The tip revisits the same points in space hundreds of times with intermittent injection to create a continuous knot written with aqueous fluorescent microsphere suspension in aqueous granular gel (UV illumination, side and top views). (C) Writing structures atop a fluorescence microscope during live imaging allows a detailed study of yielding length scales and time scales. (D) The granular gel flow speed along the axis of translation is plotted normalized by the translation speed. Disturbances in flow decay within less than one tip diameter (see fig. S2). (E) A hemispherical cap made from uncrosslinked 1-μm microspheres, created 6 months before photographing, exhibits long-term stability provided by the granular gel medium.

  • Fig. 3 Writing solid shells and capsules.

    (A) A thin-shell model octopus is made from multiple connected hydrogel parts with a complex, stable surface before polymerization. (B) A fluorescence image of the octopus model after polymerization, still trapped in granular gel, exhibits no structural changes from the polymerization process. (C) The polymerized octopus model retains integrity after removal from the granular gel, shown floating in water. (D) A model jellyfish incorporates flexible high aspect ratio tentacles attached to a closed-shell body. (E) Freely floating in water, the jellyfish model exhibits robustness and flexibility. (F) Model Russian dolls demonstrate the ability to encapsulate with nested thin shells. Photographs in (A), (C), and (E) were illuminated with white light, and those in (B), (D), and (F) were illuminated with UV light, shown with false-color look-up table (LUT) to enhance weak features.

  • Fig. 4 Hierarchically branched tubular networks.

    (A and B) A continuous network of hollow vessels with features spanning several orders of magnitude in diameter and aspect ratio (insets: confocal cross sections). (C) A high-resolution photo of truncated vessels around a junction shows hollow tubes with thin walls and features about 100 μm in diameter. (D) Junctions exhibit stable concave and convex curvatures. (E) A crosslinked network, removed from the granular gel, photographed freely floating in water (inset: confocal cross section).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/8/e1500655/DC1

    Materials and Methods

    Fig. S1. Granule size.

    Fig. S2. Microscopic imaging of writing in the granular gel medium.

    Fig. S3. Tip speed, injection rate, and feature width.

    Fig. S4. Scaling and limits of feature width.

    Fig. S5. Rheological characterization of the granular gel medium.

    Fig. S6. Stable writing in the granular gel medium.

    Fig. S7. Writing with rheologically disparate materials.

    Fig. S8. Writing with living cells.

    Movie S1. Microscopic imaging of writing in the granular gel medium.

    Movie S2. Writing nested Russian dolls in the granular gel medium.

    Movie S3. Writing a knot in the granular gel medium.

    Movie S4. Chiral rod array written in the granular gel medium.

    Movie S5. Model octopus shell structure.

    Movie S6. Model jellyfish structure with flexible, solid tentacles.

    Movie S7. Hierarchically branching tubular network.

    Movie S8. Freely floating branched network.

    Movie S9. Cell migration and division in the granular gel medium.

  • Supplementary Materials

    This PDF file includes:

    • Materials and Methods
    • Fig. S1. Granule size.
    • Fig. S2. Microscopic imaging of writing in the granular gel medium.
    • Fig. S3. Tip speed, injection rate, and feature width.
    • Fig. S4. Scaling and limits of feature width.
    • Fig. S5. Rheological characterization of the granular gel medium.
    • Fig. S6. Stable writing in the granular gel medium.
    • Fig. S7. Writing with rheologically disparate materials.
    • Fig. S8. Writing with living cells.
    • Legends for movies S1 to S9

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov format). Microscopic imaging of writing in the granular gel medium.
    • Movie S2 (.mov format). Writing nested Russian dolls in the granular gel medium.
    • Movie S3 (.mov format). Writing a knot in the granular gel medium.
    • Movie S4 (.mov format). Chiral rod array written in the granular gel medium.
    • Movie S5 (.mov format). Model octopus shell structure.
    • Movie S6 (.mov format). Model jellyfish structure with flexible, solid tentacles.
    • Movie S7 (.mov format). Hierarchically branching tubular network.
    • Movie S8 (.mov format). Freely floating branched network.
    • Movie S9 (.mov format). Cell migration and division in the granular gel medium.

    Files in this Data Supplement:

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